VMS Help TCPIP Services, Programming Interfaces, Sockets API, $ASSIGN, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    The $ASSIGN system service establishes a path to a device but
    does not check whether the calling process has the capability
    to do I/O operations to the device. The device drivers may apply
    privilege and protection restrictions. The calling process must
    have NETMBX privilege to assign a channel.
    System dynamic memory is required for the target device, and the
    I/O byte limit quota from the process buffer is used.
    When a channel is assigned to the TCPIP$DEVICE: template network
    device, the network software creates a new device called BGn,
    where n is a unique unit number. The corresponding channel number
    is used in any subsequent operation requests for that device.
    When the auxiliary server creates a process for a service with
    the LISTEN flag set, the server creates a device socket. In
    order for your application to receive the device socket, assign
    a channel to SYS$NET, which is the logical name of a network
    pseudodevice, and perform an appropriate $QIO(IO$_SETMODE)
    operation.
    Channels remain assigned either until they are explicitly
    deassigned with the Deassign I/O Channel ($DASSGN) service or,
    if they are user-mode channels, until the image that assigned the
    channel exits.